Typically, a silver halide photographic element, after exposure, is developed, fixed, washed and dried. In the development step, the latent image formed by the exposure of the photosensitive silver halides is converted into a visible image. In the fixing step the undeveloped silver halides are washed out. In the case of an element for color photography, the exposed element is color developed and the processing also comprises a bleaching step in which the developed silver is eliminated, so that the processed element contains no more than a dye image. The bleaching and fixing steps can be combined in a single bleaching/fixing step. In practice, the element to be processed is in the form of a strip of film which, from a feed reel, is transported successively by means of conveying rollers through processing tanks containing respectively developing, bleaching, fixing, stabilizing, stop and washing solutions.
In the case of the printing and photographic processing of motion picture films, it is necessary to circulate at speeds which are sometimes high (several thousands of meters per hour), hundred of meters of film delivered by storage or feed reels or "coils"having a diameter ranging up to 50 cm or more. These large quantities, large-diameter coils and high feed rates give rise to tensions and friction which are themselves responsible for the formation of static electricity. The accumulation of the static charges is responsible for the attraction and accumulation of dust on the surface of the film. This is prejudicial to the quality of the surface state of the film when the latter is subjected to mechanical stresses during reprinting and copying. In addition, when handling the coils, this accumulation of charges can cause an electrical discharge, and produce a spark causing fog on the exposed film, if this incident occurs before development.
This phenomenon of the accumulation of charges, known as electrostatic charging, is well known in photography. A very large number of antistatic substances have been tried for reducing electrostatic charging and its effects. Such substances are described in Research Disclosure, September 1994, Photographic Silver Halide Emulsions, Preparations, Addenda, Systems and Processing, IX-C, page 520.
In photography, antistatic substances must obviously help to reduce the electrostatic charges, including in a dry atmosphere. On the other hand, they must not interfere with the other constituents of the photographic material or with the substances acting during photographic processing. Different antistatic agents are known and can be used during the manufacture of a photographic film. However, at the time of development and use of the developed film, protection by the antistatic agents initially incorporated during the manufacturing of the film has become insufficient in the majority of cases and, in particular, in the case of motion picture films.
The object of the present invention is a method for solving these problems by providing improved antistatic protection for a photographic film at the time of its processing.